As a metal material of a rubber-metal complex such as oil seal, gasket, diaphragm, valves, etc., which are required to have water resistance, LLC (long life coolant) resistance and heat resistance, a stainless steel has been mainly used.
Even when a rubber metal laminated plate is tried to be prepared by directly applying a vulcanizing adhesive to stainless steel and adhering rubber thereto, there is a problem that liquid resistant adhesion durability is poor. Also, when a dipping test of this rubber metal laminated plate is carried out by using water, LLC, etc., there is a problem that it causes adhesion peel.
To solve the above problems, the applicant of the present invention has previously proposed that a coating type chromate treatment is applied on a stainless steel as a pre-treatment before coating with a vulcanizing adhesive, whereby resistances to water, LLC, etc., are improved (Patent Document 1, Patent Document 2).
However, according to the coating type chromate treatment, Cr6+ ion is contained therein so that it is not preferred for environmental reasons.
To the contrary, various kinds of undercoating agents for a vulcanizing adhesive comprising a phenol series resin as a base material have been commercially available.
However, such an undercoating agent does not show sufficient adhesiveness and water resistance with regard to adhesion with stainless steel.
Thus, the applicant of the present invention has further proposed various vulcanizing adhesive compositions comprising an alkoxysilane as an adhesive of a metal and rubber for manufacturing a rubber-metal complex.
These vulcanizing adhesive compositions are particularly suitable for adhesion of a metal surface which has been subjected to a chemical or physical surface treatment in advance, but when they are applied to a non-treated metal surface, as much adhesion as a surface treated metal cannot be obtained, an example of which is stainless steel treated with coating type chromate.
Also, in an actual use environment, there are many cases in which different kinds of metals are contacted to each other simultaneously in the state of dipping in the same solution. In such a case, an electrical potential is generated between the stainless steel plate which forms a rubber metal laminate and the different kind of the metal contacting thereto, and a phenomenon can be seen that adhesion peeling or generation of blister (bubble) is promoted (Patent Documents 3 to 12).
To solve these problems, it has been proposed to use a metal surface treatment agent containing an organometallic compound and silica (Patent Document 13).